The present invention relates to the field of manufacturing articles with structured surfaces. More particularly, the present invention provides tooling with undulating helical coils for manufacturing articles with one or more structured surfaces and methods of using the tooling to manufacture articles with one or more structured surfaces.
Articles with one or more structured surfaces find a variety of uses. The articles may be provided as films that exhibit, e.g., increased surface area, structures used to provide a mechanical fastener, optical properties, etc. When these films are manufactured for use as mechanical fasteners, the protrusions that are found on the structured surface are commonly referred to as hooks. The hooks may be formed in a curved shape or they may be substantially upright stems that are deformed in a subsequent operation to include, e.g., a head in the shape of mushroom.
Mechanical fasteners are sometimes designed so that two hook strips can be used to fasten two articles together by adhering each strip to one of the articles and then interengaging the two strips. Such a mechanical fastener is shown in U.S. Pat. No. 3,192,589 (Pearson) which calls the fastener xe2x80x9chermaphroditicxe2x80x9d because its headed studs have both male and female characteristics when intermeshed. The Pearson fasteners can be made by molding a base from which integral headless studs project and then heat softening the tips of the studs.
U.S. Pat. No. 5,077,870 (Melbye et al.) discloses one method of manufacturing the hook strip portion of a mechanical fastener by forcing molten material into cavities formed in a moving mold surface. The stems formed by the moving mold surface are then capped to form the desired fasteners. The cavities are formed in the mold surface by drilling. As a result, the cavities are cylindrical in shape and, although some precision can be obtained in depth, diameter and spacing between cavities, it is obtained with some difficulty and increased costs. Furthermore, damage to the mold surface typically requires that the entire mold be discarded.
U.S. Pat. No. 5,792,411 (Morris et al.) discloses a molding tool manufactured by laser machining a mold surface. Molten material is then forced into the cavities in the moving mold surface to form stems. The stems are then capped to form the desired fasteners. Because the cavities are formed by laser ablation, the cavity shape is based on the energy distribution within the laser beam used to form the cavities. Furthermore, precise control over the depth of the cavities is difficult to obtain due to variability in the material used to construct the mold, the power of the laser beam, the energy distribution within the beam, beam focus, etc.
U.S. Pat. No. 4,775,310 (Fischer) and PCT Publication No. WO 97/46129 (Lacey et al.) disclose tooling used to manufacture hook strips for a hook-and-loop style mechanical fastener. The tools are formed by a hollow drum with a water cooling jacket. A series of mold disks or alternating mold disks and spacer plates are laminated together along the length of the drum to form the desired mold cavities on the face of the roll. Disadvantages of these designs include the cost of manufacturing the mold disks with adequate precision to ensure that the mold cavities are of the same depth, length, spacing, etc. Size limitations imposed on the disks by manufacturing difficulties can, in turn, limit line speed in processes using the tools. Other disadvantages of this design include non-uniform cooling of the mold cavities, non-uniformities in the products produced by the stacked plates, etc.
The present invention provides tool rolls and methods of using the tool rolls to manufacture articles with one or more structured surfaces. The tool rolls include an outer surface that, when used in connection with materials of the proper viscosity or formability, can form a structured surface on an article. Because the tools are manufactured in roll-form, they can be advantageously used in continuous manufacturing processes. Alternatively, discrete articles may be processed using the tool rolls of the present invention.
By xe2x80x9cstructured surfacexe2x80x9d it is meant that a surface of the article deviates from a planar or other smooth surface. For example, the structured surface may include protrusions extending therefrom, such as stems used in connection with mechanical fasteners. Other alternative structured surfaces include, but are not limited to: continuous grooves or ridges, elongated structures, etc.
The tool rolls of the present invention are constructed of a cylindrical base roll and are wrapped with one or more continuous wires in an undulating helical pattern. The wires are used, in essence, to form a structured surface on the tool roll that is the negative of the structured surface to be formed on the articles processed using the tool roll. In one embodiment, at least one of the wires wound around the base roll may include a plurality of voids formed therein that, when wound about the base roll, form a plurality of mold cavities on the outer surface of the tool roll. Alternatively, the one or more wound wires may be used to form a continuous structured surface, e.g., a continuous groove or grooves.
The undulating helical coils formed by the wires in tool rolls of the present invention present a profile or shape such that the distance between a reference plane transverse to the longitudinal axis of the base roll and the wire or wires sequentially increases and decreases at least once when moving in one direction about a circumference of the base roll. As a result, although the wire or wires wrapped about the base roll progress across the face of the roll, they undulate to provide the desired varying distance between to the reference plane. The undulating helical pattern formed by the wire or wires may be provided by a winding surface proximate the end or ends of the base roll.
Advantages of this undulating helical winding design may include, for example, more even distribution of wear on any surfaces (e.g., a nip roll) against which the tool roll is biased during operation. Another potential advantage may be found in varying the orientation of any mold cavities (relative to the machine direction) formed in the tool roll by the wound wire or wires. Any protrusions formed in a structured article by the mold cavities may then also vary in their orientation relative to the machine direction. Yet another potential advantage of the undulating helical winding on tool rolls of the present invention is that rotation of the windings relative to the base roll may be inhibited.
Other advantages of the tool rolls include, but are not limited to the ability to replace the wire windings on the base roll if the outer surface of the tool roll becomes damaged or worn. The tool rolls may also be relatively inexpensive as compared to the cost of manufacturing tool rolls using, e.g., stacked plates or direct drilling of the mold surface.
Another advantage is the ability to control the spacing between mold cavities along the width of the roll by varying the thickness of the wire or wires wrapped around the base roll. Spacing of the mold cavities about the circumference can also be independently controlled by controlling the spacing between voids in the wire or wires wrapped around the base roll. A further advantage is that, by controlling the profile or cross-sectional shape of the wire or wires and the shape or shapes of the voids formed in the wire, variations in the shape or shapes of the mold cavities can also be achieved.
Yet another advantage of the present invention is the relatively small thermal mass of the wire or wires wrapped around the base roll in comparison to the thermal mass of the base roll. As a result, thermal control over the mold cavities can be improved, which can result in corresponding improvements in the uniformity of the products produced using the tool rolls.
As used in connection with the present invention, a xe2x80x9cmold cavityxe2x80x9d may be any discontinuity in an otherwise smooth or planar surface into which moldable material may flow during a molding process. In some embodiments of the present invention, the tool rolls may include mold cavities with high aspect ratios as defined below, although it should be understood that a mold cavity need not have a high aspect ratio.
In one aspect, the present invention provides a tool roll including a cylindrical base roll having first and second ends spaced apart along a longitudinal axis; and a first wire with a plurality of first voids formed therein, the first wire being wound in helical coils around the base roll, wherein the plurality of first voids in the first wire form a plurality of first cavities, each cavity of the plurality of first cavities including an opening at an outer surface of the tool roll; wherein a distance between the first wire and a reference plane transverse to the longitudinal axis of the base roll sequentially increases and decreases at least once when moving in one direction about a circumference of the base roll.
In another aspect, the present invention provides a tool roll including a cylindrical base roll having first and second ends spaced apart along a longitudinal axis; a first wire with a plurality of first voids formed therein, the first wire being wound in helical coils around the base roll; a second wire wound around the base roll, wherein the second wire is located between adjacent helical coils of the first wire; wherein the second wire and the plurality of first voids in the first wire form a plurality of first cavities, each cavity of the plurality of first cavities including an opening at an outer surface of the tool roll; and wherein a distance between the first wire and a reference plane transverse to the longitudinal axis of the base roll sequentially increases and decreases at least once when moving in one direction about a circumference of the base roll.
In another aspect, the present invention provides a method of forming a structured surface on an article by providing a tool roll including a cylindrical base roll having first and second ends spaced apart along a longitudinal axis, a first wire with a plurality of first voids formed therein, the first wire being wound in helical coils around the base roll, wherein the plurality of first voids in the first wire form a plurality of first cavities, each cavity of the plurality of first cavities including an opening at an outer surface of the tool roll, wherein a distance between the first wire and a reference plane transverse to the longitudinal axis of the base roll sequentially increases and decreases at least once when moving in one direction about a circumference of the base roll. The method also includes contacting a moldable material to the outer surface of the tool roll to form the structured surface using the outer surface of the tool roll, the moldable material at least partially filling at least some of the first cavities; and removing the structured surface from the outer surface of the tool roll, wherein the structured surface includes a plurality of protrusions corresponding to the plurality of first cavities.
In another aspect, the present invention provides a method of forming a structured surface on an article by providing a tool roll including a cylindrical base roll having first and second ends spaced apart along a longitudinal axis, a first wire wound in helical coils around the base roll, wherein a distance between the first wire and a reference plane transverse to the longitudinal axis of the base roll sequentially increases and decreases at least once when moving in one direction about a circumference of the base roll, a second wire wound in helical coils around the base roll, wherein the second wire is located between adjacent helical coils of the first wire, and wherein the helical coils of the first and second wires alternate along the longitudinal axis, and further wherein a height of the first wire above the base roll is less than a height of the second wire above the base roll, whereby a helical groove is formed on an outer surface of the tool roll, the helical groove conforming to the shape of the first wire. The method further includes contacting a moldable material to the outer surface of the tool roll to form a structured surface on an article using the outer surface of the tool roll, the moldable material at least partially filling at least a portion of the helical groove formed by the first and second wires; and removing the structured surface from the tool roll, wherein the structured surface includes a series of ridges.
These and other features and advantages of the present invention are described below in connection with illustrative embodiments of the present invention.